Select the most appropriate option to fill in the blank no. 6.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. Problem.
- In the passage, the sentence discusses the difficulty in solving the problem of the common cold despite progress in other areas of medicine. The most appropriate word here should describe the challenge or difficulty related to the common cold.
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"Problem" is the most fitting choice because it directly addresses the issue of the common cold being difficult to solve.